Recently, a global trend toward stricter quality regulation values for petroleum products (hydrocarbon oils) has emerged to improve atmospheric environments. For example, a reduction of sulfur compounds in gas oils is desirable because sulfur may adversely affect the durability of after-treatment apparatus expected to provide effective control of diesel emissions, such as oxidation catalysts, nitrogen oxide (NOx) reduction catalysts, and continuous regeneration-type filters for removing particulate matter from diesel exhausts.
Under these circumstances, develop of a technique of ultra-deep desulfurization for reducing most of the sulfur compounds in a hydrocarbon oil is being regarded as important. A possible technique generally usable for reducing the sulfur compounds of a hydrocarbon oil is to use severer operating conditions for hydrodesulfurization, e.g., reaction temperature and liquid hourly space velocity. However, when reaction temperature is elevated, a carbonaceous matter precipitates on the catalyst and hence catalytic activity rapidly decreases. Moreover, use of a lowered liquid hourly space velocity results in a decreased purification ability although desulfurization is enhanced, so that it becomes necessary to enlarge the scale of the facility.
Consequently, the best way of attaining the ultra-deep desulfurization of a hydrocarbon oil without using severer operating conditions is to develop a catalyst having an excellent desulfurization activity.
Many investigations are recently being made on various subjects such as the kinds of active metals, methods of active-metal impregnation, improvements of catalyst supports, regulation of catalyst pore structures, and activation methods, and the following results of development have been reported and known on novel deep desulfurization of a gas oil as one example.
For example, there has been known a process for producing a catalyst which comprises impregnating a support with a solution containing a compound of a metal in the Group 6 of the periodic table (hereinafter simply referred to as “Group 6 metal”), a phosphorus component, a compound of a metal in the Group 8 of the periodic table (hereinafter simply referred to as “Group 8 metal”), and an organic acid, followed by drying at a temperature of 200° C. or lower (see, Patent Documents 1 and 2).
Moreover, there has been known a catalyst containing an oxide support and a salt or complex of a Group 8 metal selected from cobalt and nickel and a heteropolyacid of a Group 6 metal selected from molybdenum and tungsten thereon, wherein a concentration of the Group 8 metal is from 2 to 20% by weight in the basis of the support, a concentration of the Group 6 metal is from 5 to 50% by weight in the basis of the support, and free water is substantially not present (see. Patent Document 3).
Furthermore, there has been known a catalyst comprising a support and a Group 6 metal and a Group 8 metal thereon, which is obtained by adding a hydroxycarboxylic acid in an amount of 0.3 to 5.0 equivalents to total number of moles of the Group 6 metal and the Group 8 metal, followed by drying at a temperature of 200° C. or lower (see, Patent Document 4).
As above, there have been proposed various catalysts and processes for producing the same and also proposed catalysts having higher desulfurization activity which can be produced in a simple and convenient manner and with which the ultra-deep desulfurization of a hydrocarbon oil can be realized without using severer operating conditions. However, it is still desired to develop a catalyst having further improved activity and a longer catalyst life.
Patent Document 1: JP-A-2003-299960
Patent Document 2: WO04054712A1
Patent Document 3: JP-A-6-31176
Patent Document 4: Japanese Patent No. 3244692